1. Field of the Invention
The present invention relates to apparatus for coupling optical energy from a fiber to a hybrid circuit of the type that includes at least one electro-optic element. More particularly, this invention pertains to an optical interface arrangement that facilitates the complete fabrication and testing of such a hybrid package prior to engagement to the pigtail of an optical fiber conductor.
2. Description of the Prior Art
Optical networks often include hybrids. Hybrid integrated circuits consist of a combination of two or more integrated-circuit types or one integrated-circuit type and discrete elements. Opto-electronic hybrid circuits often include photodetectors for converting an optical signal delivered by an optical fiber network to a corresponding electrical signal. Photodetector devices may be of various compositions including silicon, indium, gallium arsenide, and gallium arsenide with cadmium sulfide. Many precision applications require that the hybrid circuit elements be contained or enclosed within a hermetically-sealed case. The fabrication of such circuits commonly includes a bakeout process prior to sealing for purifying the sealed environment within the case by outgassing such contaminants as hydrocarbons, EPOXY resins and solder flux.
In conventional optical networks that include electro-optical hybrids, an optical fiber conductor is coupled to the hybrid package through a ferrule in the side of the hybrid case. The connection of the optical fiber to the hybrid occurs prior to device testing and bakeout. The specifications for bakeout can be stringent, particularly in military applications. The outgassing of substantial amounts of contaminants can significantly lengthen manufacturing processes.
Optical fibers are typically encapsulated in jackets of acrylic plastic material of limited temperature tolerance. Generally such material should not be subjected to temperatures in excess of 105 degrees Centigrade for the most common fiber jackets. This can significantly affect (lower) the temperature of bakeout in conventional arrangements wherein the fiber is fixed to the hybrid case. As a result, the time required for environmental purification is affected (lengthened). At the present time, bakeout for a hybrid with fiber pigtail attached typically requires an eight (8) hour process. Furthermore, since circuit testing is forestalled until bakeout has been completed, device yield is yet even more significantly limited.